Pumps of the above-mentioned kind are now commonly used in vacuum sewage systems onboard ships, aero planes and trains. However, such systems are also increasingly being used on land due to reduced water requirement and easy handling and treatment of waste water, as well as its flexibility as regards installation of piping and layout given by such systems.
The applicant of the present application introduced in 1987, cf. EP Patent No. 0287350, for the first time the novel vacuum sewage system where the vacuum in the system was generated by means of a liquid ring screw pump of this kind where the pump is used as well to discharge the sewage from a vacuum tank or the like to which it is connected.
EP Patent No. 0454794, also filed by the applicant, further shows a revolutionary improvement of a vacuum sewage system where the liquid ring screw pump is provided with a grinder or macerator and is connected directly with the suction pipe of the system, whereby vacuum is generated in the sewage suction pipe and sewage is discharged directly from the system by means of the pump.
The present invention may, or may not include such grinder provided at the inlet end of the Archimedes screw rotor.
Liquid ring screw pumps of the above-mentioned type commonly comprise a housing with a suction inlet part at one end and a pressure outlet part at the other end and within the housing rotatably provided Archimedes screw (screw rotor) which is driven by an electric motor via a shaft. In the known prior art pump and motor, as for instance shown in the above EP Patent No. 0454794, the rotor is commonly provided at or close to the centre axis of the pump housing.